Jacinda Ardern's dramatic pregnancy fight revelation

Jacinda Ardern has revealed she discovered her pregnancy after a fight with her partner Clarke Gayford.

The Prime Minister was being interviewed by Kiwi musician Gin Wigmore for an episode of Sitting Room Only when she spilled the beans on the dramatic moment.

Ardern says she was in the middle of coalition negotiations, and had just had an argument with Gayford.

"I was in Wellington, and Clarke [Gayford] was in Northland and he was doing his fishing show," Ardern says.

"I'd called him and we'd had a little bit of an argument about whether or not he was going to be able to get to Wellington for the announcement of who was going to form the Government."

That same day she realised she was pregnant - leading to an awkward scene with her partner.

"Later on in the evening when I got the result of my test I thought, 'oh my word, I'm going to have to call him back'," she says.

"And I called him back, and he was kind of exasperated because I had just got off the phone to him, and he was surrounded by his whole film crew. And so he went into a toilet, so he was in a rented bach, in a toilet, when I told him."